Toxoplasma gondii is a ubiquitous intracellular protozoan parasite that is a major opportunistic infection in immunocompromised individuals, the cause of congenital toxoplasmosis in newborns and recently has been identified as a potential bioterrorism agent (list B). Cytokines play an important role in the regulation of T. gondii in the central nervous system. Interferon-gamma (IFN() is the main cytokine controlling replication of T. gondii in the brain. The investigator's previous studies defined that IFNgamma significantly inhibits the replication of T. gondii in astrocytes. The mechanism of IFNgamma in astrocytes was found to be independent of all of the known anti-Toxoplasma effector mechanisms. However, the investigator recently determined that IFNgamma mediated inhibition in astrocytes was reversed in astrocytes deficient in the GTP binding protein, IGTP (deltaIGTP). The function of IGTP is not known but it is thought to be involved in regulation of the vesicular trafficking pathway. Preliminary microarray studies of IFNgamma induced gene expression in astrocytes indicate that host cell cholesterol metabolism is altered in IFNgamma treated astrocytes. T. gondii has recently been shown to require cholesterol uptake from the host cell. Effects on lipid and cholesterol trafficking to the parasitophorous vacuole may be the mechanism of IFNgamma inhibition in astrocytes. As IFNgamma dependent mechanism(s) play a major role in controlling T. gondii in the brain, understanding these mechanism(s) remains an important challenge in understanding disease pathogenesis. In this project the mechanism(s) of IFNgamma induced inhibition in astrocytes will be investigated. The specific aims of this proposal are: 1) Identify the IFNgamma response genes in wild type and IGTP knockout (deltaIGTP) astrocytes via microarray analysis, 2) Characterize the effect of IFNgamma on the establishment of the parasitophorous vacuole in astrocytes and 3) Investigate the hypothesis that IFNgamma inhibition is mediated by affecting vesicular trafficking and/or cholesterol trafficking to the parasitophorous vacuole and that IGTP is involved in regulating this trafficking.